Also if this helps, I actually used an example from Serious Sam Forever (credit goes to the guys that invented the bullet holes in SSF) but I copied it to my stone material in databases (only the decal particle) and did few changes to it. Also I'm using my own texture for bullet decals. (The bullet holes don't flicker and they are finished in SSF)

2. Bugged Dynamic Shadows of Players

So, I converted the Double Shotgun from SS1 and well, I have shadow problems now with any other weapon.
What I mean is that the shadow shows the players shadow but doesn't do the same for weapon, it looks on the shadow like the weapon is cut in half.

1. Bullet Holes
Well, flickering is usually a sign of "poly-fighting", where two polygons exist in essentially the same place and "fight" to be viewed by observers. For a solution, adjust the "Relative placement" of the bullet hole particles to appear away from the ground a short distance.

2. Bugged Dynamic Shadows of Players
This is due to the bounding box of the player model not encompassing the weapon completely. Normally, the Sam model's bounding box is extended in front to support weapons such as the Minigun, but that doesn't seem to be the case with the Sam model you're using. To fix it, change the bounding box of the Sam model to fit what I've described above.

1. Bullet holes
well, flickering is usually a sign of "poly-fighting", where two polygons exist in essentially the same place and "fight" to be viewed by observers. For a solution, adjust the "relative placement" of the bullet hole particles to appear away from the ground a short distance.

2. Bugged dynamic shadows of players
this is due to the bounding box of the player model not encompassing the weapon completely. Normally, the sam model's bounding box is extended in front to support weapons such as the minigun, but that doesn't seem to be the case with the sam model you're using. To fix it, change the bounding box of the sam model to fit what i've described above.